The present invention relates to an exhaust gas filter for collecting carbon particles in exhaust gases discharged from an internal combustion engine, particularly a diesel engine of an automobile or the like.
Conventionally, such a filter as described above has been formed of a honeycomb structure provided with a large number of axially extending passages which are defined by separator walls, for example.
However, in this conventional filter, the major part of the carbon particles pass through the passages without interfering with the surfaces of the separator walls.
Therefore, the exhaust gas purifying efficiency is low.
In order to solve the above described problem, an exhaust filtration device is proposed in U.S. Pat. No. 4,276,071. This device is composed of a ceramic monolith provided with a plurality of inlet passages and a plurality of outlet passages, which are defined by a plurality of porous thin walls. The inlet passages are open at the inlet end of the monolith and closed at the outlet end thereof while the outlet passages are closed at the inlet end of the monolith and open at the outlet end thereof.
According to this device, the exhaust gases enter the inlet passages and flow into the adjacent outlet passages, passing through the porous walls. And the purified exhaust gases are discharged from the outlet passages. Therefore, the filtration area of this device for the exhaust gases is high so that the exhaust gas purifying efficiency can be improved.
However, in this device, pressure loss of the exhaust gases rapidly increases when the porous walls begin to be clogged by the carbon particles.
Accordingly, one object of the present invention is to provide an exhaust gas filter having a honeycomb structure for purifying exhaust gases with a high particulates collecting efficiency, without an increment in pressure loss of the exhaust gases.
Another object of the present invention is to provide an exhaust gas filter provided with porous thin separator walls defining inlet passages into which the exhaust gases enter and outlet passages from which the exhaust gases are discharged, and means for preventing the pressure loss of the exhaust gases from increasing.